Resin board, manufacturing process for resin board, connection medium body, circuit board and manufacturing process for circuit board

ABSTRACT

A compression function layer  60  is provided on at least one board surface. The compression function layer  60  adds a function of being compressed by receiving pressure in the direction of the board thickness to the resin board  10  which includes this layer. Thereby a sufficient pressure is applied to conductors  14.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a resin board which is used as acircuit board, a connection medium body, a manufacturing process for aconnection medium body a circuit board and a manufacturing process for acircuit board.

[0003] 2. Description of the Related Art

[0004] In recent years, together with the miniaturization, reduction ofweight, increased functionality and increased performance of electronicdevices, the demand has become strong, concerning industrial applicationas well as concerning application in the broad field of consumerdevices, for a multi-layer circuit board on which semiconductor chipssuch as LSIs can be mounted in high density at an inexpensive price.

[0005] A resin multi-layer circuit board which can be supplied lessexpensively than a ceramic multi-layer board and which can fulfill theabove described market demand has attracted attention as a substitutefor a conventional ceramic multi-layer board and technologicaldevelopment has been carried out to develop a resin multi-layer circuitboard that is a board suitable for high density mounting.

[0006] As a resin multi-layer circuit board developed in this manner, acircuit board of an any layer inner via hole construction has beendisclosed in Japanese Unexamined Patent Publication No. Hei 06-268345(1994). This circuit board is a resin multi-layer board using acomposite material of aramid non-woven fabric reinforcing material andan epoxy resin as the insulating layer and, therefore, can be suppliedat a comparatively inexpensive price. In addition, this circuit boardadopts the any layer inner via hole construction, that is to say, aninterstitial via hole connection construction which can connectarbitrary positions in wiring layers through conductive paste and,therefore, becomes suitable for high density mounting.

[0007] A circuit board of the any layer inner via hole constructionhaving the above characteristics cannot be formed unless a prepreg isused which has voids in the inside due to the impregnation of resin intoa non-woven fabric. That is to say, this circuit board has aconstruction which can be implemented only by using a particularmaterial.

[0008] However, in addition to a higher density of mounting, today,market demands have become as follows. That is to say, market demandsare manifold and there are demands such as a circuit board of a lowdielectric constant suitable for a high speed circuit network, a circuitboard of a high heat resistance, and the like. Therefore, it is requiredto implement a circuit board which has characteristics that fulfillrespective desires and suitable for high density mounting.

SUMMARY OF THE INVENTION

[0009] Accordingly, the main purpose of the present invention is toprovide a circuit board which can implement a low connection resistanceand an excellent connection stability.

[0010] In order to achieve the above described purpose, the presentinvention provides a compression function layer on at least one boardsurface to gain a resin board used in an insulating layer of a circuitboard or a connection medium body. The compression function layer hascharacteristics such that it adds the function of being compressed byreceiving pressure in the direction of the thickness to a resin board ora medium connection body.

[0011] According to the present invention, a circuit board which adds acompression function and implements a low via connection resistance andan excellent connection stability can be gained without being limited toa specific combination of materials and, rather, can be gained by makingthe surface have specific characteristics.

[0012] The compression function layer is preferably a porous layer.Then, by controlling the degree of invasion of a resin component of theresin board into the porous layer, the function of being compressed byreceiving pressure in the direction of thickness can be added to theresin board.

[0013] The porous layer has a hole group wherein the hole group ispreferably formed of a plurality of holes which are connected to eachother so that both ends of the hole group have openings on both sides ofthe porous layer. Then, air held in the holes can be ejected to theoutside through pressure in the direction of the board thickness.Thereby, it can be made easier for the resin component of the resinboard to invade into the porous layer and the amount of invasion of thisresin component to the porous layer can be easily controlled byadjusting the pressure.

[0014] The above described compression function layer can also be formedof a layer of insulating particles which is provided on a resin board orconnection medium body in the condition protruding from the boardsurface. In this case, the insulating particles protruding from theboard surface are pressed into the resin board by receiving pressure inthe direction of the board thickness and, thereby, the compressionfunction can be added to the resin board.

[0015] The resin board is preferably in a semi-cured condition on, atleast, the surface on which the compression function layer is provided.Then, because of the semi-cured condition of the board material,advantages are gained as follows. That is to say, in the compressionfunction layer made up of a porous layer, it becomes easier for a resincomponent to invade into the porous layer. In addition, in thecompression function layer made up of insulating particles, it becomeseasy to press insulating particles into the resin board.

[0016] The resin board is preferably provided with a protective filmlayer so as to be removable as an additional layer above the abovedescribed compression function layer. Thereby, during a manufacturingstep for a circuit board using the resin board or the connection mediumbody, dust from the outside can be prevented from becoming attached tothe compression function layer. In addition, the entire thickness of theresin board or the connection medium body can be adjusted through theaddition or removal of a protective film layer. Thereby, it becomespossible to add a compression margin at the time when conductorsprovided through the resin board or the connection medium body in thedirection of the thickness is compressed.

[0017] A resin board of the present invention can be manufactured asfollows. That is to say, after a porous layer is provided on at leastone board surface of a resin board, the above described porous layer isadhered to the above described resin board through pressure by applyingpressure to the above described resin board of the degree that a resincomponent of the above described resin board does not invade into theholes of the above described porous layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The other purposes of the present invention will become evidentby understanding the below described embodiments and are clearly shownin the attached claims. And, those skilled in the art will perceive anumber of advantages that are not touched on in the presentspecification in the case that this invention is implemented.

[0019]FIG. 1A is a cross sectional view showing a construction of aresin board 10A according to the first preferred embodiment of thepresent invention;

[0020]FIG. 1B is a cross sectional view showing a construction of aresin board 10B according to the first preferred embodiment of thepresent invention;

[0021]FIG. 2A is a cross sectional view showing a manufacturing processfor a resin board 10A;

[0022]FIG. 2B is a cross sectional view showing a manufacturing processfor a resin board 10B;

[0023]FIG. 3A is a cross sectional view showing a construction of aresin board 30 according to the second preferred embodiment of thepresent invention;

[0024]FIG. 3B is a cross sectional view showing a construction of theresin board 30 in the compressed condition;

[0025]FIG. 3C is a cross sectional view showing another construction ofthe resin board 30;

[0026]FIG. 4 is a cross sectional view showing a construction of a resinboard 50 according to the third preferred embodiment of the presentinvention;

[0027]FIG. 5 is a cross sectional view showing a construction of aconnection medium body 12 according to the fourth preferred embodimentof the present invention;

[0028]FIGS. 6A and 6B are cross sectional views respectively showing thesteps in a manufacturing process for a double surface board 17 accordingto the fifth preferred embodiment of the present invention;

[0029]FIGS. 7A and 7B are enlarged cross sectional views of a main partshowing, respectively, the condition of a resin component 58 flowinginto recesses 51;

[0030]FIG. 8 is a plan view showing the relationships between themaximum diameter L of a hole 104 and the minimum separation interval Sof conductors 14;

[0031]FIGS. 9A and 9B are cross sectional views showing, respectively,the steps in a manufacturing process for a double surface circuit boardusing a wiring layer with carriers;

[0032]FIGS. 10A to 10D are cross sectional views showing, respectively,the steps in a manufacturing process for a double surface circuit board17 using protective film layers;

[0033]FIGS. 11A and 11B are cross sectional views showing, respectively,the steps in a manufacturing process for a multi-layer board;

[0034] FIGS. 12A-1 to 12D are cross sectional views showing,respectively, the steps in another manufacturing process for the doublesurface circuit board;

[0035]FIGS. 13A and 13B are cross sectional views showing, respectively,the steps in another manufacturing process for the multi-layer board;

[0036]FIGS. 14A to 14C are cross sectional views showing, respectively,the steps of the first half in still another manufacturing process forthe multi-layer board; and

[0037]FIGS. 15A and 15B are cross sectional views showing, respectively,the steps of the second half in the manufacturing process directly abovefor the multi-layer board.

DETAILED DESCRIPTION OF THE INVENTION

[0038] In the following, the preferred embodiments of the presentinvention are described in reference to the drawings.

[0039] (First Preferred Embodiment)

[0040]FIGS. 1A and 1B are cross section schematic views showing a resinboard 10 of the present embodiment.

[0041] Resin boards 10A and 10B have porous layers 11 on the surfaces.That is to say, the difference between the resin boards 10A and 10B ofthe present embodiment and a conventional resin board is whether or nota porous layer 11 which becomes a compression function layer is placedon a surface and the resin boards 10A and 10B of the present embodimenthave porous layers 11 on, at least, one surface.

[0042] Though in the configurations of FIGS. 1A and 1B, the porouslayers 11 are provided, respectively, on both sides of the boards 10Aand 10B shown as examples, in the case that where a porous layer isprovided on only one side, a resin board of the present invention can begained.

[0043] As for the board material of the resin boards 10A and 10B of thepresent embodiment, a prepreg 100 wherein thermosetting resin isimpregnated into a fiber material for reinforcement or an adhesive sheet101 can be used. An example wherein the prepreg 100 is used is the resinboard 10A shown in FIG. 1A while an example where the adhesive sheet 101is used is the resin board 10B shown in FIG. 1B.

[0044] As for the prepreg 100, a glass epoxy prepreg, an aramid epoxyprepreg, or the like, can be cited. The glass epoxy prepreg is gained byimpregnating an epoxy resin in a semi-cured (B stage) condition into aglass non-woven cloth. The aramid epoxy prepreg is gained byimpregnating an epoxy resin in a semi-cured condition into an aramidnon-woven cloth. Here, the epoxy resin in the semi-cured condition hasadhesive properties. Therefore, in these prepregs 100 it is notnecessary to provide an adhesive layer for adhering the porous layer 11to the surface of the prepreg 100 as shown in FIG. 1A.

[0045] The adhesive sheet 101 is a film board made of thermoplasticresin or a thermosetting resin such as a polyimide, a liquid crystalpolymer, an aramid or a PTFE (poly-tetra-fluoro-ethylene). As for theresin board 10B made of the adhesive sheet 101, as shown in FIG. 1B, anadhesive layer 102 made of a thermosetting resin or a thermoplasticresin is provided on the surface of the adhesive sheet 101 where aporous film is formed.

[0046] The types of thermosetting resin or thermoplastic resin(hereinafter referred to as a prepreg impregnation resin) which areimpregnated into the prepreg 100 or the resins forming the adhesivelayer 102 which is provided to the adhesive sheet 101 can be selectedaccording to the combinations of the resin boards 10A, 10B and the metalused for wiring layers (described below) and are not particularlylimited.

[0047] As described below, however, it is necessary to make an adhesiveor a prepreg impregnation resin invade into the inside of the spaces ofthe porous layers 11 from the surrounding area. In order to make theseresins invade into the porous layers 11, it is necessary for the prepregimpregnation resin or the adhesive layer 102 to maintain fluidity duringthe step. Therefore, in the case of a thermosetting resin, it is used ina semi-cured condition. In addition, in the case of a thermoplasticresin, it is made fluid by adjusting the temperature at the time of thestep wherein the adhesive is made to flow at the softening temperaturepoint, or greater.

[0048] As for the concrete materials for the prepreg impregnation resinor the adhesive layer 102, the following can be cited. That is to say, athermosetting resin or a thermoplastic resin such as an epoxy resin, apolyimide resin, a phenol resin, a fluorine resin, an unsaturatedpolyester resin, a PPE (poly-phenylene-ester) resin, a bismaleimidetri-azine resin, a cyanate-ester resin can be cited. Here, in the casethat a film board of a thermoplastic resin is used as the adhesive sheet101, the film board itself has adhesive properties at the softeningtemperature point, or greater and, therefore, the film board itself canalso be made to serve as an adhesive layer.

[0049] At least one board surface of the resin board 10A, 10B formed inthe above manner is provided with a porous layer 11. The porous layer 11is a compression function layer which adds the function of beingcompressed by receiving pressure in the direction of the thickness tothe resin board 10A, 10B. As for a concrete example of the porous layer11, a porous sheet of a PTFE (poly-tetra-fluoro-ethylene), a polyimide,an aramid, or the like, or a porous ceramic can be cited.

[0050] These porous layers 11 can provide microscopic holes from 1 μm,or less, to several μm in the inside thereof. In addition, in that casethe size of the holes can be controlled in a highly precise manner.

[0051] It is preferable to provide a compression function layer made ofthe porous layer 11, of which the dielectric constant is small such as aPTFE (poly-tetra-fluoro-ethylene) at the time of the manufacturing of acircuit board used for a high frequency circuit from the followingpoints of view.

[0052] That is to say, since the magnetic flux density leaking from thewiring layer is high, the effect of the dielectric loss of thedielectric constant is larger in the surface layer portions closest tothe wiring layer of the resin board 10A or 10B than in the inside of theresin board 10A or 10B. Therefore, in the case that the compressionfunction layer of the porous layer 11, or the like, provided in thesurface portions of the resin board 10A or 10B is formed of a lowdielectric constant material, a high frequency characteristic in acircuit board made of the resin board 10A or 10B can be increased. Inaddition, by providing the porous layer 11, the mechanical strength ofthe resin board 10A or 10B can be reinforced.

[0053] The porous layers 11 have a plurality of hole groups 103 in theinside thereof. The hole groups 103 are formed by a plurality of holes104 connected to each other. At least one of these hole groups 103 hasopenings on both sides of a porous layer 11 on both edges thereof, thatis to say, at least one hole group 103 exits from among the hole groups103 which is in a non-sealed condition that is not sealed in the porouslayer 11. Both sides of the porous layer 11 are mutually connectedthrough the hole group(s) 103 formed in the above manner.

[0054] Next, manufacturing processes for the resin boards 10A and 10Bare described in reference to FIG. 2. FIG. 2A shows a manufacturingprocess for the resin board 10A while FIG. 2B shows a manufacturingprocess for the resin board 10B.

[0055] Manufacturing processes for both of the resin boards 10A and 10Bare essentially the same. That is to say, compression function layersare layered on both sides of the prepreg 100 or on the adhesive sheet101 so as to be integrated. Concretely, the porous layers 11 are adheredby applying heat and pressure to both sides of the prepreg 100 or to theadhesive sheet 101. Adhesion by applying heat and pressure can becarried out by, for example, rotating a heated roller in the conditionwhere it is pressed onto the porous layers 11. Here, at the time ofadhesion by applying heat and pressure, the pressure applied to theresin board 10A or 10B is to the degree where the resin components ofthe resin board 10A or 10B hardly invade into the holes 104 of theporous layers 11. Here, the resin components of the resin board 10A or10B mean resin components forming the impregnation resin of the prepreg100 or forming the adhesive layer 102.

[0056] At the time when the porous layers 11 are adhered to the resinboard 10A or 10B through pressure, a protective film layer may besimultaneously formed so as to be removable on, at least, one boardsurface of the resin board 10A or 10B. In this case, a porous layer 11is formed on the protective film layer in advance and, after the porouslayer 11 is arranged so as to contact a side of the resin board 10A or10B, the protective film layer is adhered through pressure and, thereby,a resin board having a protective film layer and a porous layer 11 canbe manufactured simply with a smaller number of manufacturing steps. Asfor the conditions of adhesion through pressure at this time, thefollowing conditions can, for example, be set. That is to say, in thecase that a PET film (thickness 4 μm to 25 μm) is adhered to a glassepoxy prepreg or to an aramid epoxy prepreg through pressure, thefeeding speed of the roller heated to the temperature of 100° C. to 140°C. can be set at 1 m/sec to 3 m/sec and the air pressure can be set at0.5 kgf/cm² to 5.0 kgf/cm². The protective film layer and the porouslayer 11 may, of course, be formed on both sides of the resin board 10Aor 10B. However, an asymmetric arrangement is, of course, possiblewherein the porous layer 11 and the protective film layer are bothprovided on only one of the board surfaces of the resin board 10A or 10Bwhile only the protective film layer is provided on the other boardsurface.

[0057] (Second Preferred Embodiment)

[0058] A resin board 30 according to the second preferred embodiment ofthe present invention is described in reference to FIG. 3. FIG. 3A is across section schematic view showing the resin board 30 which has aninsulating particle layer 32 that becomes a compression function layer.

[0059] The present embodiment is formed in the same manner as the firstpreferred embodiment except for that the porous layers 11 in the firstpreferred embodiment are changed to the insulating particle layers 32.

[0060] An insulating particle layer 32 can be formed as follows. That isto say, by adding a plurality of insulating particles 31 to an adhesivelayer 102′ in the resin board 10B made of the adhesive sheet 101described in the first preferred embodiment, the insulating particlelayer 32 can be formed of this adhesive layer to which the insulatingparticles are added.

[0061] As for the details, the insulating particle layer 32 is formed byadding insulating particles 31 such as silica, alumina or aluminumhydroxide to the adhesive layer 102′. Then, an insulating particle layer32 formed in this manner is formed on, at least, one board surface ofthe resin board 10B. At this time, some insulating particles 31 are inthe condition of protruding from the surface of the adhesive layer 102′.

[0062] In the resin board 30 which has such an insulating particle layer32, as shown in FIG. 3B, the insulating particles 31 are pressed intothe inside of the adhesive layer 102′ in the subsequent heat compressionstep. Thereby, the resin board 30 is compressed.

[0063] In the case that a similar insulating particle layer to the abovedescribed insulating particle layer 32 is provided when the resin board30 is formed by using the resin board 10A made of the prepreg 100described in the first preferred embodiment, the following may becarried out.

[0064] That is to say, as shown in FIG. 3C, a resin including insulatingparticles 31′ is used for the resin impregnated into a cloth or anon-woven cloth which becomes a reinforcing material in the prepreg 100.As a concrete example of such a resin board 30′, a glass epoxy prepregincluding fillers can be used wherein an epoxy resin in which silicaparticles are diffused is impregnated into a glass cloth.

[0065] (Third Preferred Embodiment)

[0066] The third preferred embodiment of the present invention isdescribed in reference to FIG. 4. FIG. 4 is a cross section schematicview showing a resin board 50 which has recesses 51 that function ascompression function layers on the surfaces. That is to say, thedifference between the resin board 50 of the present embodiment and aconventional resin board for a circuit board is whether or not a surfacehas a recess 51 and the resin board 50 of the present invention has, atleast, one recess 51 on at least one board surface. Though in FIG. 4 anexample is shown wherein a plurality of recesses 51 are provided on bothsides, the case wherein the recesses are provided on only one side orthe case wherein only one recess is provided can also be assumed to bethe resin board 50 of the present embodiment.

[0067] As described below, the forms or the number of recesses 51 arenot particularly limited but, rather, the total volume of the entiretyof the recesses becomes important.

[0068] As for the material of the resin board 50 of the presentembodiment, the same material as resin boards 10A, 10B and 30 in thefirst and second embodiments can be used.

[0069] A method for creating the recesses 51 is not particularly limitedand, for example, an adhesive layer is formed on a support body on whichprotruding parts corresponding to the recesses 51 are provided and,then, after transcribing the adhesive layer onto a film board, therecesses can be created by removing the support body. As for theadhesive layer, a thermosetting adhesive or a thermoplastic adhesive canbe used. In the case of a thermosetting adhesive, it is transcribed in asemi-cured condition to create recesses while, in the case of athermoplastic adhesive, it is heated to the softening temperature point,or greater, at the time of transcription for creating recesses.

[0070] In addition, as for another method for creating recesses 51,there is the following method. That is to say, a flat adhesive layer isformed on a film board in advance and, by using a metal mold to whichprotruding parts are provided corresponding to the positions of therecesses 51, pressure is applied to the mold so as to be pressed to theadhesive layer in a semi-cured condition. After that, by removing themold, the recesses 51 of a desired size and shape can be provided ondesired positions of the adhesive sheet. In addition, in the case of athermoplastic adhesive, the mold is pressed while being heated to thesoftening temperature point, or greater.

[0071] It is preferable to carry out a mold releasing process in theparts of the above described support body or adhesive layer whichcontact the adhesive layer. Then, the adhesive becomes easier to bereleased from the support body or from the mold so that manufacturing aresin board 50 of the present embodiment becomes easier. In addition, inthe method for creating recesses 51 with the above described supportbody or mold, the form, the number, the intervals, or the like, of therecesses 51 can be arbitrarily selected.

[0072] As for another method for creating recesses 51, there is thefollowing method. That is to say, after preparing a solution wherein athermosetting adhesive is diluted by a solvent, a supersonic vibrationis given to the solution so as to cause bubbles. The solution containingbubbles is applied to a film board. Then, by drying the solutioncontaining bubbles on the film board, the solvent is volatilized to bein a semi-cured condition. Thereby, the bubble portions become holes soas to create the recesses 51.

[0073] As for an example of such a method, there is the followingmethod. That is to say, a supersonic vibration (38 kHz, 150 W) is givento a THF (tetra-hydroxy-furan) solution (30 wt % of solids) of apolyimide-based adhesive so that bubbles are caused. Then, the solutionis applied to a film board 13 μm thick) made of polyimide by a gapcoater and is dried for one minute at 120° C. Thereby, recesses 51 areformed in the dried solution. The thickness of the solution after beingdried is approximately 6 μm.

[0074] Furthermore, as for another method for creating recesses 51,there is the following method. That is to say, a light sensitiveadhesive layer is formed in a flat manner on a film board in advance.This adhesive layer is covered with a mask which corresponds to therecesses 51 of a desired form and size followed by exposure fordeveloping the non-cured portions. Thereby, recesses 51 are created inthe adhesive layer. In this case, the adhesive layer is left in asemi-cured condition. According to this method recesses 51 can becreated in a comparatively easy manner.

[0075] In the case of a resin board 50 made of a prepreg, recesses 51can be created by a similar method to a resin board made of an adhesivesheet.

[0076] In addition, in the case of the resin board 50 made of a prepreg,since the resin which is contained has adhesive properties, recesses 51can be created in the resin of the surface layer without forming anadhesive layer. The recesses 51 can be created in a similar manner byusing the above described support body or metal mold.

[0077] In addition, in the case of a prepreg, recesses 51 can be createdthrough a conventional manufacturing step. That is to say, in amanufacturing process for a resin board 50 using a prepreg, first, areinforcing material in a sheet form such as a glass cloth or aramidpaper is soaked in a solution distilled by a solvent so as to have thedesired viscosity and, thereby, a resin board 50 is manufactured. Then,an extra solution is removed from the manufactured resin board 50 bymeans of a roller, or the like, and, in addition, the board is dried inorder to remove the extra solvent. In such a processing step, the resinboard 50, before being dried, is passed through a roller which isprovided with protruding parts corresponding to the recesses 51.Thereby, the resin board 50 which has recesses 51 on the surface can beeasily manufactured.

[0078] In addition, in a manufacturing process for a resin board 50 byusing a prepreg, recesses 51 can be created as follows. That is to say,the board undergoes sudden heating and drying treatments in the dryingstep for removing the extra solvent. Thereby, holes are created, afterthe solvent has been removed therefrom, in the surface of the resinboard 50 and these holes become the recesses 51.

[0079] As an example of such a manufacturing process, there is thefollowing method. That is to say, an MEK (methyl-ethyl-ketone) solution(60% solids) of an epoxy resin composition for prepreg impregnation isimpregnated in an aramid non-woven cloth (basis weight of 72 g/m², 120μm thick) and, thereby, a resin board 50 is manufactured. Then, theresin board 50 is passed between a pair of rollers which have a gap of150 μm and, thereby, an extra solution is squeezed out from the resinboard 50. After that, the resin board 50 is placed in a dryer which isheated to 200° C. for three minutes. Thereby, recesses 51 are created inthe resin board 50.

[0080] According to this method no extra steps are necessary forproviding the recesses 51 so that the resin board 50 can beinexpensively manufactured.

[0081] In the case of the resin board 50 of the present embodimentwherein an adhesive layer is formed on one side or on both sides of afilm board, recesses 51 can be created. That is to say, in the step ofdrying after applying an adhesive layer, holes are caused by suddenlyheating and drying the board in the same manner as in the above so thatrecesses 51 are created in the resin board 50.

[0082] (Fourth Preferred Embodiment)

[0083] Next, a structure of a medium connection body 12 used in theresin boards 10A, 10B, 30 and 50, described in the first to the thirdpreferred embodiments, is described in reference to FIG. 5. Here, in theconnection medium body 12 described in the present embodiment inreference to FIG. 5 or in the circuit board described in the belowdescribed embodiment, any of the resin boards 10A, 10B, 30 and 50 can beused as a resin board. Therefore, the resin boards 10A, 10B, 30 and 50are generally referred to as a resin board 10 in the description belowor in the figures referred to in the description. In addition, since theporous layer 11, the insulating particle layer 32 or the recesses 51 allfunction as compression function layers, the porous layer 11, theinsulating particle layer 32 or the recesses 51 are all referred to ascompression function layer 60 in the description below or in the figuresreferred to in the description.

[0084] The medium connection body 12 is formed by creating through holes13 in desired positions of a resin board 10 and, after that, by fillingthese through holes 13 with conductors 14 as shown in FIG. 5. Theconductors 14 become interstitial via holes.

[0085] As for the conductors 14, conductive paste which containsconductive powder in a resin binder can be used. The conductive pasteincreases its conductivity through the application of compression.

[0086] As for the conductive powder, a powder is used made of, at least,one type of metal selected from among gold, silver, copper, nickel,palladium, lead, tin, indium and bismuth, an alloy of these or a mixtureof these. In addition, coat fillers made by coating spheres made of themetal or alloy, oxides such as alumina or silica or organic synthesizedresin with the above described metal or alloy may be used as theconductive powder.

[0087] The form of the conductive powder is not particularly limited andmay be a powder, a fiber, granules, spherical balls, or a mixture ofthese.

[0088] As for the resin used as the resin binder, an epoxy resin in aliquid form, a polyimide resin, a cyanate ester resin, a phenol resolresin, or the like, is used.

[0089] As for the epoxy resin, a glycidyl-ether-type epoxy resin such asa bisphenol-A type epoxy resin, a bisphenol-F type epoxy resin or abisphenol-AD type epoxy resin or an epoxy resin which has two, or more,epoxy groups such as an alicyclic epoxy resin, a glycidyl-amine-typeepoxy resin, a glycidyl-ester-type epoxy resin, or the like, is used.

[0090] An additive of a solvent or a dispersion agent such asbutyl-cellosolve, ethyl-cellosolve, butyl-carbitol, ethyl-carbitol,butyl-carbitol-acetate, ethyl-carbitol-acetate and α-terpineol can, ifnecessary, be contained in the above described resin.

[0091] In addition, the conductors 14 are not limited to the abovedescribed conductive paste but, rather, a connection material forinterstitial via holes of the type which can gain conductivity throughcontact by being compressed such as via posts made of a metal such asgold, silver, copper, nickel, palladium, lead, tin, indium and bismuthcan be used without a particular limitation.

[0092] In the creation of the interstitial via holes in the connectionmedium body 12, first, through holes 13 are created in desired positionsof the resin board 10. As for the method for creating the through holes13, a conventional hole processing method for circuit boards, a laserprocessing method by using a carbonic acid gas laser or a YAG laser or amechanical processing method such as drilling or punching can be used.

[0093] In particular, in the case that through holes 13 are created bymeans of a heat processing laser processing method, the surroundingwalls of the through holes 13 can be melted. At this time, in the casethat the compression function layer 60 is formed of the porous layer 11,it becomes as follows. That is to say, holes 104 of the porous layer 11positioned in the surrounding walls disappear due to the melting of thesurrounding walls of the through holes. The holes 104 positioned in thesurrounding walls of the through holes can become places into whichleaking occurs at the time when the conductive paste filled in withinthe through holes leaks into the surrounding area. Therefore, when theholes 104 of these places are made to disappear, the paste can beprevented from leaking.

[0094] However, it is not necessary to completely compress the holes104. The holes 104 may be compressed to a size such that the conductivepowder does not enter into the holes and, thereby, above-describedeffect of preventing the paste from leaking can be gained and, inaddition, the following effect can be gained. That is to say, in theabove case resin components in the conductive paste enter into the holes104 which are allowed to remain in the condition where they becomesmaller and, as a result, the compression of the conductive paste filledinto the through holes 13 is increased so that the resistance of theconductive paste (conductors 14) can be lowered.

[0095] Next, conductors 14 are filled into the through holes 13 so thatthe connection medium body 12 shown in FIG. 5 is completed.

[0096] A printing method is used in order to fill in the conductors 14.At this time, a resin board 10 in which through holes 13 are created isplaced on a vacuum absorption support via a sheet of paper so that theconductors 14 are filled in through printing. Then, when the connectionmedium body 12 is compressed during the below described manufacturingstep for a circuit board, the density of the conductive particles filledin can be further increased. This is because resin components in theconductive paste 14 are forcefully absorbed into the sheet of paper dueto absorption by vacuuming and due to capillary action caused in thesheet of paper and, thereby, the density of the conductive powder filledin is enhanced and gaps are caused among conductive powder particles.

[0097] (Fifth Preferred Embodiment)

[0098] Next, the structure of a circuit board using the connectionmedium body 12 described in the fourth preferred embodiment and themanufacturing process thereof are described. First, a manufacturingprocess for a two-sided circuit board 17 is described in reference toFIG. 6.

[0099] As shown in FIG. 6A, metal foils 15 for forming wiring layers areoverlapped on both sides of the connection medium body 12, which isheated and compressed for adhesion. The conditions for the adhesionthrough heating and compression differ depending on the structure of theutilized material. For example, in the case that the resin substrate 10wherein an adhesive layer 102 (approximately 6 μm thick) made of apolyimide-based resin is formed on the resin board 10 made of apolyimide film board (13 μm thick), the board is heated and iscompressed for one hour at pressure of 50 kgf/cm² and at a temperatureof 200° C.

[0100] As for the metal foils 15, copper foils such as an electrolyticcopper foil or a rolled copper foil used for a conventional circuitboard are used. Though the thickness of the metal foils 15 are notparticularly limited, an electrolytic copper foil of 3 μm to 70 μm isreadily available and is preferable.

[0101] In the above described processing steps, metal foils 15 and theconnection medium body 12 are adhered through heating and compression.Next, as shown in FIG. 6B, the metal foils 15 are processed into wiringlayers 16 which have desired wiring patterns. Thereby, the two-sidedcircuit board 17 is completed. As for the processing of the wiringlayers 16, a photolithographic method, which is used in a conventionalcircuit board manufacturing, can be used.

[0102] In such a manufacturing process for a two-sided circuit board 17,at the time when the metal foils 15 undergo heating and compressionprocessing, the connection medium body 12 is compressed so that thethickness thereof becomes thinner due to the function of the compressionfunction layer 60. Thereby, the conductors 14 are simultaneouslycompressed, together with the compression of the connection medium body12, so that the conductivity thereof is enhanced.

[0103] First, a compression addition in the case where the compressionfunction layer 60 is formed of the porous layer 11 is described. In thiscase, the resin components of the surface portions of the resin board 10have fluidity and, therefore, pressure is applied to connection mediumbody 12 in the direction of the thickness and the above described resincomponents are impregnated into a hole group 103 within the porous layer11 so that the porous layer 11 sinks into the resin board 10B and of theconnection medium body 12 is compressed so that the thickness becomesthinner by the amount of sinkage. Thereby, the conductors 14 aresimultaneously compressed, together with the compression of theconnection medium body 12, so that the conductivity thereof is enhanced.

[0104] Next, a compression addition in the case that the compressionfunction layer 60 is formed of the insulating particle layer 32 isdescribed. In this case, insulating particles 31 are pressed into theinside of the adhesive layer 102′ in the heating and compression step.Thereby, the resin board 30 is compressed and the thickness of theconnection medium body 12 becomes thinner by the amount of compression.Thereby, the conductors 14 are simultaneously compressed together withthe compression of the connection medium body 12 so that theconductivity thereof is enhanced.

[0105] Next, a compression addition in the case that the compressionfunction layer 60 is created from the recesses 51 is described. In thiscase, the recesses 51 disappear in the heating and compression step.Thereby, the resin board 50 is compressed and the thickness of theconnection medium body 12 becomes thinner by the amount of compression.Thereby, the conductors 14 are simultaneously compressed together withthe compression of the connection medium body 12 so that theconductivity thereof is enhanced. That is to say, as shown in FIGS. 7Aand 7B, the recesses 51, into which the resin components 52 flow intofrom the surrounding areas, carries out the function of compressing theconnection medium body 12 (resin board 50). In this case, it isimportant to control the entire volume of the recesses 51. In detail,the ratio of the entire volume of the recesses 51, which is occupied inthe connection medium body 12, to the entire volume of the connectionmedium body 12 (entire volume of recesses 51/entire volume of connectionmedium body 12) is required to be equal to the compression ratio of theconnection medium body 12.

[0106] It is preferable to set the compression ratio of the conductors14 as follows. That is to say, in the case that the conductors 14 areused as interstitial via holes, a compression ratio of 5%, or higher, ispreferable. It is possible to secure the conductivity of theinterstitial via holes with a compression ratio of less than 5%.However, in the case of 5%, or higher, a sufficient pressure is appliedto the contact portions among conductive powder particles as well as tothe contact portions between the conductive powder particles and themetal foils 15 so as to ensure strong adhesion. Thereby, the connectionresistance of the interstitial via holes is lowered. In addition, thestability of the connection is increased.

[0107] The two-sided circuit board 17 manufactured in this manner hasthe following structure. That is to say, the resin board 10 has thecompression function layer 60 on, at least, one board surface. The resinboard 10 has through holes 13 in the thickness direction. Conductors 14are filled into the through holes 13. Wiring layers 16, which havedesired wiring patterns, are provided on both sides of the resin board10. The wiring layers 16 on both sides of the resin board 10 areelectrically connected to each other through the conductors 14.

[0108] In the case that the two-sided circuit board 17 is formed, thefollowing is preferable. That is to say, as shown in FIG. 8, it ispreferable to make the maximum diameter L of the holes 104, which arecomponents of the hole group 103, smaller than the minimum separationinterval S of the conductors 14. In this manner it becomes as follows.

[0109] The conductive paste forming the conductors 14 invades into holes104 by receiving pressure and a short circuit among the conductors 14,due to the conductive paste which has invaded into the holes 104, can beprevented by setting the maximum diameter L as described above.

[0110] In the present embodiment, by combining the compression additioneffect of the compression function layer 60 and another technology, thecompression power can be further enhanced.

[0111] For example, during the step of heating and compression the resinboard 10, with the metal foils 15 being overlapped, wiring layers 16,which are formed in advance, are pressed into the connection medium body12 instead of the metal foils 15, that is to say, a so-calledtranscription method is used.

[0112] In detail, as shown in FIG. 9, a so-called wire layer withcarrier wherein a wiring layer is formed on a support board 20 can beused. As an example of a wiring layer with carrier, there is an aluminumcarrier on which a wiring layer is layered via a mold releasing layer.

[0113] That is to say, as shown in FIG. 9A, a wiring layer 21 is formedby etching a copper foil layered and placed on the support board 20 forpatterning by using a ferric chloride solution, an ammonium persulfatesolution, or the like. Then, as shown in FIGS. 9A and 9B, after layeringthe wiring layer 21 so as to be buried in the connection medium body 12,the support body 20 is removed through etching by means of hydrochloricacid.

[0114] By using a transcription method, the pressure applied to theconductors 14 in the connection medium body 12 becomes the sum of thepressure due to the porous layer 11 and the pressure due to the pressedin wiring layer 21.

[0115] In addition, by using a compressible base material within whichthere are holes as the resin board 10′, a greater pressure can beapplied to the conductors 14 due to the synergetic effects withcompression addition effect of the porous layer 11 according to thepresent invention. As for such a resin board 10′, a porous film ofpolyimide or of fluorine resin can be cited.

[0116] In addition, as shown in FIG. 10, by making the conductors 14filled into the through holes 13 protrude from the surface of theconnection medium body 12, the pressure applied to the conductors 14through heating and compression can be further enhanced. This isdescribed in the following.

[0117] First, as shown in FIG. 10A, a protective film layer 22 made of afilm material such as PET (polyethylene-terephthalate), PEN(polyethylene-naphthalate), or the like, and upon which is carried out amold releasing process (for example, a process using a silicon-basedmold releasing agent), is attached to the surface which the boardcontacts, is attached to, at least, one surface of the resin board 10which has the compression function layer 60. In the case that theprotective film layer 22 is formed of these materials, the protectivefilm layer 22 can be attached to the resin board 10 so as to beremovable.

[0118] Next, as shown in FIG. 10B, through holes 13 are created in theresin board 10, which includes the protective film layer 22. Then,through a printing method conductors 14 are filled into the throughholes 13. At this time the protective film layer 22 works as a maskwhich prevents the conductors 14 from becoming attached to undesirableportions. Furthermore, the conductors 14 which are filled into thethrough holes 13 are increased in size by the thickness of theprotective film layer 22.

[0119] Next, as shown in FIG. 10C, when the protective film layer 22 isremoved, the connection medium body 12 wherein the conductors 14protrude from the through holes 13 is gained. Metal foils 15 areattached to both sides of the resin board 10 in this condition. Then,the metal foils 15 and the resin board 10 are integrated by adhesionthrough heating and compression. At this time, the conductors 14protrude from the through holes 13 and, thereby, the portions of theconductors 14 which protrude work during heat compression step so as toenhance the pressure to the conductors 14.

[0120] Finally, by patterning the metal foils 15 in thephotolithographic step, the metal foils 15 are converted to the wiringlayers 16 which have desired wiring patterns. Thereby, the two-sidedcircuit board 17 shown in FIG. 10D is gained. In this two-sided circuitboard 17 the connection reliability of the interstitial via holes isenhanced to a degree equal to the enhanced pressure applied to theconductors 14.

[0121] In the above manner, the connection medium body 12 or thetwo-sided circuit board 17 are formed and in the case that a multi-layercircuit board is manufactured by using these connection medium body 12or the two-sided circuit board 17, the process becomes as follows.

[0122] As shown in FIG. 11A, the above described two-sided circuit board17 or a core board 18 made of a conventional two-sided circuit boardsuch as a glass epoxy board is prepared. Then, the connection mediumbody 12 is overlapped on the wiring layer 16 of the prepared core board18 and a metal foil 15 is overlapped on top of that so as to be adheredthrough heating and compression. Thereby, the core board 18, theconnection medium body 12 and the metal foil 15 are integrated. Here, itis preferable to use the connection medium body 12 wherein conductors 14slightly protrude from the medium body surface. Thus the pressureapplied to the conductors 14 can be further enhanced.

[0123] Furthermore, the metal foil 15 is processed into the wiring layer16 by means of photolithographic method. Thereby, the multi-layercircuit board shown in FIG. 11B is completed. Here, by repeating thismethod, a number of layers of a circuit board can be easilymanufactured.

[0124] Next, another manufacturing process for a two-sided circuit boardor a multi-layer board is described in reference to FIGS. 12 and 13.

[0125] First, a resin board 10 wherein a compression function layer 60is attached to at least one board surface and a wiring layer 21 which issupported by a support board 20 are prepared. Then, a protective filmlayer 22 is attached to one board surface of the resin board 10. Here,the protective film layer 22 may be provided on the surface on which thecompression function layer is placed or may be provided on the surfaceon which the compression function layer is not placed. In FIG. 12, as anexample, the protective film layer 22 is provided on the surface onwhich the compression function layer is placed.

[0126] Next, as shown in FIGS. 12A-1 and 12A-2, a wiring layer 21 isplaced on the surface on which the protective film layer is not placedof the resin board 10. At this time, the wiring layer 21 is positionedwith respect to the resin board 10 before it is placed on the board.Here, as shown in FIG. 12A-2, the wiring layer 21 may be placed in thecondition where it is partially sunk into the resin board 10 through acompression process. Contrarily, as shown in FIG. 12A-1, the wiringlayer 21 may be placed in the condition where it rests on the surface ofthe resin board 10 without carrying out a compression process. In thecase that the wiring layer 21 is placed on the resin board 10 in thecondition where it rests on the board surface, the wiring board 21 willbe made to sink into the resin board 10 through the below described heatcompression step and at that time, the pressure applied to theconductors 14 ca be enhanced.

[0127] Next, through holes 13 are created in the resin board 10. Thethrough holes 13 are created in the direction of the thickness so as toreach to the wiring layer 21 starting from the surface on which theprotective film layer is placed. At this time, the through holes 13 arecreated in the condition where they are positioned with respect to thewiring layer 21. The through holes 13 can be created by means of a laserprocessing method using a carbonic acid gas laser, a YAG laser, anexcimer laser, or the like. In particular, in the case that the throughholes 13 are created by means of heat processing laser processingmethod, the surrounding walls of the through holes 13 can be melted. Atthis time, in the case that the compression function layer 60 is formedof a porous layer 11, it becomes as follows. That is to say, holes 104of the porous layer 11 positioned in the surrounding walls disappear dueto the melting of the surrounding walls of the through holes. The holes104 positioned in the surrounding walls of the through holes can becomeplaces into which leaking occurs at the time when the conductive pastefilled in within the through holes leaks into the surrounding area.Therefore, when the holes 104 of these places are made to disappear, thepaste can be prevented from leaking.

[0128] However, it is not necessary to completely compress the holes104. The holes 104 may be compressed to a size such that the conductivepowder does not enter into the holes and, thereby, above-describedeffect of preventing the paste from leaking can be gained and, inaddition, the following effect can be gained. That is to say, in theabove case resin components in the conductive paste enter into the holes104 which are allowed to remain in the condition where they becomesmaller and, as a result, the compression of the conductive paste filledinto the through holes 13 is increased so that the resistance of theconductive paste (conductors 14) can be lowered.

[0129] After creating the through holes 13, as shown in FIG. 12B,conductors 14 made of conductive paste are filled into the through holes13. At the time of the filling in of the conductors 14, in the case thata pressure reduction treatment is applied to the through holes 13 at thetime of the filling in or after the filling in, bubbles can be preventedfrom remaining within the through holes. Such a pressure reductiontreatment leads to the high density filling in of the conductors 14.

[0130] After filling in the conductors 14, the protective film layer 22is removed. Then, as shown in FIG. 12C, a metal foil 15 is placed on thesurface of the resin board 10 from which the protective film layer hasbeen removed and an adhesion treatment through heating and compressionis applied. As for the condition of the adhesion treatment throughheating and compression, the conditions of the adhesion treatmentthrough heating and compression for a conventional circuit board can beused. For example, the conditions of 180° C. to 250° C., 30 kgf/cm² to200 kgf/cm², 0.5 hours to 2.0 hours can be used.

[0131] Finally, the metal hole 15 is processed to a wiring layer 16which has desired wiring patterns by means of a photolithographicmethod. Then, the support board 20 is removed. Thereby, the two-sidedwiring board 17 shown in FIG. 12D is completed.

[0132] Since the conductors 14 can be formed according to the positionof the wiring layer 16 in the above method, the positioning precisionbetween the wiring layer 16 and the conductors 14 is increased.

[0133] In the case that a multi-layer board is formed, it ismanufactured as follows.

[0134] First, a layered body shown in FIG. 13A is manufactured. This isgained by replacing the wiring layer 21 with a support board with thetwo-sided circuit board 17 shown in FIG. 12D in the structure of theresin board 10 with a wiring layer shown in FIGS. 12A-1 and 12A-2.

[0135] Then, a metal foil 15 is layered on the manufactured layeredbody. The metal foil 15 is placed on the surface of the layered body onwhich a wiring layer is not placed.

[0136] After placing the metal foil 15 on the above described layeredbody, the layered body undergoes an adhesion treatment through heatingand compression. Then, the metal foil 15 is processed to a wire layer 16which has desired wiring patterns by means of a photolithographicmethod. Thereby, a multi-layer board shown in FIG. 13B is gained.Furthermore, by repeating the above described steps, a circuit board ofan increased number of layers can be manufactured.

[0137] Still another manufacturing process for a circuit board isdescribed in reference to FIGS. 14 and 15.

[0138] First, a resin board 10 wherein a compression function layer 60and a protective film layer 22 are attached to at least one boardsurface and a core board 18 shown in FIG. 11A are prepared. Then, alayered body is formed by placing and layering the resin boards 10 onboth sides of the core board 18. Here, the resin boards 10 are layeredas follows. That is to say, the protective film layer 22 is removed fromthe surface of the resin board 10 which will contact the core boardbefore the resin board 10 is layered on the core board 18. Or the resinboard 10 is layered on the core board 18 in the condition that the resinboard 10 is placed in the direction where the surface on which theprotective film layer is not formed contacts the two-sided circuit board17.

[0139] Then, as shown in FIGS. 14A and 14B, through holes 13 are createdin the respective resin boards 10 which are placed and layered on thecore board. The through holes 13 are created in the condition where theyare positioned with respect to the wiring layers 16 which lay on thebottoms of the through holes. That is to say, the through holes 13 arecreated in the direction of the thickness of the resin boards 10 so asto reach to the wiring layers 16.

[0140] After creating the through holes 13, as shown in FIGS. 14C and15A, conductors 14 are filled into respective through holes 13. Afterthat, the protective film layers 22 are removed.

[0141] After removing the protective film layers 22, metal foils 15 (notshown) are placed on both sides of this layered body. Then, by makingthe layered body undergo an adhesion treatment through heating andcompression, the layered body and the metal foils 15 are integrated.Finally, the metal foils 15 are processed into wiring layers 16 whichhave desired wiring patterns by means of a photolithographic method.Thereby, the multi-layer board shown in FIG. 15B is completed.

[0142] Next, the reason why it is advantageous in a structure of acircuit board to provide a compression function layer of the presentinvention, represented by the porous layer 11, is described.

[0143] First, the first reason is described. In a board structurewherein interlayer connections are made of conductors, which are made ofconductive paste, it is essential to compress the conductors in somefashion. Conventionally, a prepreg having holes inside is used as theresin board and this prepreg is compressed so as to compress theconductors. That is to say, by applying pressure to the prepreg, theholes are crashed so as to shrink the dimension of the prepreg in thethickness direction and, thereby, the conductors are compressed.

[0144] In the case that a large number of holes exist inside of theresin board, however, dimensional change easily occurs due totemperature change, moisture change or external force. It is desirablefor the dimensional change during a manufacturing step for a circuitboard to be as small as possible because it is a cause of processingstep defects such as pattern shift. In this manner, holes created in theresin board itself become a factor that causes the circuit board easilychange in form, which is disadvantageous in a manufacturing step for acircuit board that requires a higher density and a higher precision inwiring.

[0145] Contrarily, as for the resin board 10 of the present inventionwherein a compression function layer 60 such as a porous layer 11 isprovided on a surface, the board itself can be formed of a resin in asolid condition (condition with non holes) and, therefore, the dimensionchange can be reduced and a higher density of the circuit board can besufficiently achieved.

[0146] Next, the second reason is described. The higher the density ismade in the circuit board, the narrower become the separation intervalsbetween the conductors. As described above in reference to FIG. 8, inthe case that holes exist among the conductors and the maximum diameterof the holes is larger than the minimum separation interval between theconductors, adjoining conductors may be short-circuited by theconductive paste which has invaded into a hole.

[0147] However, it is not easy to highly precisely control the size ofthe holes in a prepreg and, in particular, it is difficult to createmicroscopic holes in a highly precise manner. Therefore, in theconfiguration of a circuit board to which a compressibility is given bycreating holes in a prepreg, it becomes more difficult to make thediameter of the holes smaller than the separation intervals amongconductors as the density of mounting becomes higher. As a result, therisk of short-circuit between conductors due to the conductive pasteinvading into a hole increases in a circuit board of which the densityhas been made higher. In this manner, the creation of holes in the resinboard is not acceptable because as the density of mounting becomeshigher, short-circuits are increasingly caused.

[0148] Contrarily, in a resin board 10 of the present invention where acompression function layer 60 (in particular, porous layer 11) isprovided on a surface, the sizes of holes 104 can be controlled in ahighly precise manner so that microscopic holes 104 can be created in ahighly precise manner. Therefore, by providing a porous layer 11 whichhas such holes 104, a short-circuit due to the conductive paste invadinginto the holes 104 can be prevented even in the case that the density ofmounting has become higher in the circuit board.

[0149] In addition, in the case that the porous layer 11 is provided,the mechanical strength of the resin board 10 can be reinforced.

[0150] As described above, according to the present invention,advantageous effects can be gained that a resin board and a connectionmedium body provided with a low connection resistance of inner via holesand an excellent connection stability as well as a circuit board usingthe above resin board or connection medium body can be implemented.

[0151] Though this invention is described in detail with respect to themost preferred embodiment thereof, the combination and arrangement ofthe components in the preferred embodiment can be modified in a varietyof manners without deviating from the spirit and the below claimed scopeof this invention.

What is claimed is:
 1. A resin board for use as an insulating layer of acircuit board, wherein a compression function layer is provided on atleast one board surface and this compression function layer adds afunction of being compressed by receiving pressure in the direction ofthe board thickness to the resin board which includes the layer.
 2. Theresin board according to claim 1, wherein said compression functionlayer is a porous layer.
 3. The resin board according to claim 2,wherein said porous layer has a hole group so that said hole group isformed of a plurality of holes which are connected to each other andboth edges of the hole group have openings on both sides of the porouslayer.
 4. The resin board according to claim 1, wherein said compressionfunction layer is a layer of insulating particles provided in this resinboard in the condition of protruding from the board surface.
 5. Theresin board according to claim 1, wherein the resin board is in asemi-cured condition at least on the surface on which the compressionfunction layer is provided.
 6. The resin board according to claim 1,wherein a protective film layer that is removable is provided as anadditional layer above said compression function layer.
 7. A resin boardfor use as an insulating layer of a circuit board, wherein a porouslayer is provided on at least one board surface.
 8. A connection mediumbody for being provided between two wiring layers that are placed so asto face each other and for electrically connecting these wiring layers,comprising: a resin board; a compression function layer provided on atleast one board surface of said resin board; through holes created inthe direction of the thickness of said resin board; and conductorsprovided in said through holes, wherein said compression function layeradds a function of being compressed by receiving pressure in thedirection of the thickness to the connection medium body which includesthis layer.
 9. The medium connection body according to claim 8, whereinsaid compression function layer is a porous layer.
 10. The mediumconnection body according to claim 9, wherein said porous layer has ahole group so that said hole group is formed of a plurality of holeswhich are connected to each other and both edges of the hole group haveopenings on both sides of the porous layer.
 11. The medium connectionbody according to claim 8, wherein said compression function layer is alayer of insulating particles provided in said resin board in thecondition of protruding from the board surface.
 12. The mediumconnection body according to claim 8, wherein the resin board is in asemi-cured condition at least on the surface on which the compressionfunction layer is provided.
 13. A connection medium body for beingprovided between two wiring layers that are placed so as to face eachother and for electrically connecting these wiring layers, comprising: aresin board; a porous layer provided on at least one board surface ofsaid resin board; through holes created in the direction of thethickness of said resin board; and conductors provided in said throughholes.
 14. A circuit board, comprising: a resin board; a compressionfunction layer provided on at least one board surface of said resinboard; through holes created in the direction of the thickness of saidresin board; conductors provided in said through holes; and wiringlayers which are provided on both sides of said resin board and whichare electrically connected to each other via said conductors, whereinsaid compression function layer adds a function of being compressed byreceiving pressure in the board direction of the thickness to the resinboard which includes the layer.
 15. The circuit board according to claim14, wherein said compression function layer is a porous layer.
 16. Thecircuit board according to claim 15, wherein said porous layer has ahole group so that said hole group is formed of a plurality of holeswhich are connected to each other and both edges of the hole group haveopenings on both sides of the porous layer.
 17. The circuit boardaccording to claim 15, wherein the size of the holes of said porouslayer is smaller than the minimum separation interval of adjoining saidthrough holes.
 18. The circuit board according to claim 14, wherein saidcompression function layer is a layer of insulating particles providedin this resin board in the condition of protruding from the boardsurface.
 19. A circuit board, comprising: a resin board; a porous layerprovided on at least one board surface of said resin board; throughholes created in the direction of the thickness of said resin board;conductors provided in said through holes; and wiring layers which areprovided on both sides of said resin board and which are electricallyconnected to each other via said conductors.
 20. A manufacturing processfor a resin board including the step of providing a compression functionlayer on at least one board surface of the resin board.
 21. Themanufacturing process for a resin board according to claim 20, furtherincluding the step of providing a protective film layer that isremovable as a layer above said compression function layer.
 22. Amanufacturing process for a resin board including the step of providinga porous layer on at least one board surface of a resin board; and thestep of adhering said porous layer to said resin board by applyingpressure of the degree that no resin components of said resin boardinvade into the holes of said porous layer.
 23. A manufacturing processfor a circuit board comprising: the step of placing a porous layer on atleast one board surface of a resin board; the step of creating throughholes in the direction of the thickness of said resin board; the step offilling conductors into said through holes; the step of placing a wiringlayer or a metal foil on at least one board surface of said resin board;and the step of allowing the resin components of said resin board toinvade into the holes of the porous layer so as to compress said resinboard by applying pressure in the direction of the thickness to saidresin board.
 24. The manufacturing process for a circuit board accordingto claim 23, wherein a resin board where at least the surface on whichthe porous layer is provided is in a semi-cured condition is used assaid resin board.
 25. The manufacturing process for a circuit boardaccording to claim 23, wherein the step of providing a protective filmlayer on a surface of said resin board is further comprised as apretreatment of said step of creating through holes; and the step ofremoving said protective film layer is further comprised as apretreatment of said step of placing a wiring layer or a metal foil. 26.The manufacturing process for a circuit board according to claim 23,wherein the step of placing said porous layer on said resin board iseliminated by using a resin board which has said porous layer on atleast one board surface as said resin board.
 27. A manufacturing processfor a circuit board comprising: the step of placing a porous layer on atleast one board surface of a resin board; the step of placing a wiringlayer or a metal foil on first board surface of said resin board; thestep of creating through holes which reach to said wiring layer or metalfoil layer in second board surface of said resin board; the step offilling conductors into said through holes; the step of placing anotherwiring layer or another metal foil on the second board surface of saidresin board; and the step of allowing the resin components of said resinboard to invade into the holes of said porous layer so as to compresssaid resin board by applying pressure in the direction of the thicknessto said resin board.
 28. The manufacturing process for a circuit boardaccording to claim 27, wherein a resin board where at least the surfaceon which the porous layer is provided is in a semi-cured condition isused as said resin board.
 29. The manufacturing process for a circuitboard according to claim 27, wherein the step of providing a protectivefilm layer on the second board surface of said resin board is furthercomprised as a pretreatment of said step of creating through holes; andthe step of removing said protective film layer is further comprised asa pretreatment of said step of placing another wiring layer or anothermetal foil.
 30. The manufacturing process for a circuit board accordingto claim 27, wherein the step of placing said porous layer on said resinboard is eliminated by using a resin board which has said porous layeron at least one board surface as said resin board.